In an internal combustion engine mounted on a vehicle, it is a common practice that, when a throttle valve is fully closed, the fuel injection from a fuel injection valve is stopped under predetermined conditions, thereby contriving an improvement in fuel consumption. In addition, since it is desirable that a desired acceleration can be obtained when the throttle valve is again opened after the throttle valve is fully closed, the fuel injection amount is preferably correctingly increased when it is detected that the throttle valve has been again opened.
From this point of view, a fuel injection system for correctingly increasing the fuel injection amount has been proposed in Japanese Patent Laid-open No. 2000-130221 by setting a higher amount increase level as the fuel injection stop duration during the full closure period of the throttle valve has been longer when the full closure period of the throttle valve is finished.
Meanwhile, a part of the fuel injected from the fuel injection valve is adhered to the intake passage or the throttle valve, and the fuel thus adhered is sucked into the combustion chamber according to the operating cycle of the engine 12. Therefore, when the full closure period T (hereinafter referred to simply as full closure period) of the throttle valve during which the opening TH of the throttle valve is 0 is short, as shown in FIG. 7, the adhered residual amount F of the adhered fuel is comparatively large, but when the full closure period T is long, as shown in FIG. 8, the residual amount of the adhered residual amount F is very small. Therefore, it is comparatively effective to set the amount increase level to be larger as the fuel injection stop time during the full closure period is longer as shown in Japanese Patent Laid-open No. 2000-130221.
However, since the adhered fuel is sucked into the combustion chamber of the number of times of the intake stroke during the throttle full closure period, the suction amount is not necessarily determined only by the length of the fuel injection stop time during the full closure period.
The present invention has been made in consideration of the above problems. Accordingly, it is an object of the present invention to provide a fuel injection control system capable of an appropriate fuel amount increase correction for realizing a favorable acceleration performance at the time of accelerating after the full closure period of the throttle valve is finished.